Better informed individuals than little old me suggest you always change the flywheel when changing the clutch cos it must be showing some wear . Even Alex, if Im not mistaken recommends changing the flywheel and I don't get the impression he's the type to give such advice just to make a sale. He's knowledgeable regarding the Z and I for one would follow his best advice.
It makes sense anyway, how would you feel having changed only the clutch to find a few months later you still have problems and have to strip it down again. I also agree with Whacky Will regarding resale. Bite the bullet and change both you never know you may not sell it in 6 myths.
Best of luck anyway